Phosphorus nutrition of spring wheat (Triticum aestivum L.). 2.

Part I, Aust. J. Agric. Res., 1997, 48, 855-67.

. Distribution of phosphorus in glasshouse-grown wheat and the diagnosis of phosphorus deficiency by plant an

Abstract

In 2 glasshouse experiments, the effects of variations in phosphorus (P) level on concentration and distribution of total and labile P within wheat plants were examined to compare the sensitivity of various plant tests for assessing the P status of wheat.

Total P was distributed unevenly within the plant: shoots had higher total P concentrations than roots, and concentrations in grain were markedly higher than in glumes or straw. Within wheat shoots, the concentration of total and labile P varied with stage of plant growth and the type and physiological age of the plant part analysed. In general, leaf blades had higher concentrations than their subtending sheaths. During the vegetative phase, the highest P concentrations were measured in immature tissues and the concentrations decreased progressively in older plant parts, except at luxury supply where total P was invariably higher in old leaf blades.

Critical total P concentrations (CTPC) estimated for whole shoots decreased with advancing plant age beyond Zadoks Scale 13·5. Circumstantial evidence suggests that this may be caused by stems of lower P concentration progressively constituting a larger proportion of shoot biomass with increasing age.

Critical concentrations defined for leaf blades of known physiological age also decreased with plant age beyond Zadoks Scale 13·5 for both labile and total P. These decreases may result from either an increase in the size of the sampled individual leaf blades as plants age or shifts in distribution of P within the shoot from the main culm to developing tillers (or reproductive structures).

Total P is the preferred and easier method of analysis, and in most cases, diagnostic and predictive CTPC were similar in defined individual leaf blades.

The estimated critical value for the labile P: total P ratio of about 30% appeared to be independent of leaf age or stage of plant ontogeny.

These data suggest that the existence of P deficiency in wheat can be confirmed by analysing whole shoots or recently matured leaf blades for total P. In the period up until early tillering, the P test criteria are constant but thereafter must be related to stage of growth.